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Gene-sis of VAW

June 5, 2013

‘Rape’, derived from repere (Latin for seize or plunder), has been demonstrated by psychologists and sociologistsdna+vaw to be a crime of violence as opposed to an innate desire for sex. The dominant psychology behind the act of rape is to inflict fear and humiliation on the victim. Thus, rape has a strong socio–cultural underpinning, one that places burden on the nurture of an individual. However, far from being psychopathic or antisocial, rapists are “extreme” individuals who tend to blend well into their own communities. (Not surprisingly, the perpetrators are known to the victims in nearly 93% cases.) This latter aspect lends to the argument about the nature — primarily determined by the human genome — of these individuals. So, how do nature and nurture shape the rapist instincts of a few members of the society?  Do they work independently? Or one, say nature, has a stronger influence than the other?

The human genome — the complete set of human genes — comes bundled in twenty–three separate pairs of chromosomes. Of these, twenty–two pairs are numbered in approximate order of size, while the remaining pair consists of the sex chromosomes: two large X chromosomes in women, one X and one small Y (actually, the smallest) chromosome in men. A male inherits the X chromosome from his mother while the Y chromosome is handed down by the father. Genetics or the study of genome has made many startling discoveries, but nothing more astounding than the human body being effectively a vehicle for the ambitions of the genes.

Evolutionary psychologists propose that human rape appears not as an aberration but as an alternative gene–promotion strategy that is most likely to be adopted by the ‘losers’ in the competitive, harem–building struggle. If the means of access to legitimate, consenting sex is not available, then a male may be faced with the choice between force and genetic extinction. If he succeeds in impregnating one or two ‘stolen’ women before being castrated or lynched by the ‘owner’ males, then his genes (and thus behavioral tendencies) will pass on to the next generation. In A Natural History of Rape: Biological Bases of Sexual Coercion (pub. 2000), biologist Randy Thornhill and anthropologist Craig T. Palmer of the University of New Mexico expounded that rape is (in the vernacular of evolutionary biology) an adaptation encoded by genes that confers an advantage on anyone who possesses them. Back in the late Pleistocene epoch 100,000 years ago, the book contended, men who carried rape genes had a reproductive and evolutionary edge over men who did not: they sired children not only with willing mates, but also with unwilling ones, allowing them to leave more offspring (also carrying rape genes) who were similarly more likely to survive and reproduce, unto the nth generation. That would be us. And that is why we carry rape genes today. The family trees of prehistoric men lacking rape genes petered out in the natural selection process.

Subsequent scientific investigations have discredited the programmed–to–rape idea. In 2009, Sharon Bagley wrote an investigative essay in Newsweek that highlighted an anthropological study involving the Ache hunter–gatherer tribesmen of Paraguay. The Ache live much as humans did 100,000 years ago. The study concluded that reproductive costs outweigh the benefits of rape by a factor of 10 and thus could not support the “rape is selectively advantageous for procreation” theory.

Let us look into the potential genetic underpinning to rape as suggested, but not substantiated, by the evolutionary psychologists. The male rape gene would be located on the Y chromosome. Among the genes on the Y chromosome, SRY (Sex–determining region Y) gene is perhaps the most important one. It makes men into men; its gene sequence is remarkably consistent among men and has remained nearly unchanged since the last common ancestor of all people 200,000 years ago or so. Compared with other active genes, SRY is one of the fastest evolving. Its gene mutations give rise to XY females with gonadal dysgenesis (Swyer syndrome), but not rapists.

In order for the male rape gene to survive the evolution, it must offer distinct benefits to the carriers, say in reproduction. The sexual antagonism or sexual conflict theory states that when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, evolutionary arms race can potentially ensue between males and females. For instance, males may benefit from multiple mating, while multiple mating may harm or endanger females. According to the proponents of the theory, the more social and communicative a species is, the more likely it is to suffer from sexually antagonistic genes. The most social and communicative species on earth is humankind. So is the male rape gene of a sexually antagonistic variant?

Interestingly, SRY and DAX, a recently discovered gene on the short arm of the X chromosome, are antagonistic to each other. Matt Ridley discusses this antagonism in his insightful book Genome (pub. 2000). Since an X chromosome spends two–thirds of its time in females and only one–third in males, it is three times as likely to evolve the ability to ‘attack’ the Y chromosome. At the onset of the human race, the ability to seduce women might have been good for the Y chromosome. However, it came under threat from the driving X genes, so much so that it has shed as many genes as possible and has shut down the rest, to ‘run away and hide’. The great bulk of its length now consists of non–coding DNA serving no purpose at all. Then there is a small region at each tip of the Y chromosome (and correspondingly on the X chromosome), the so–called pseudo–autosomal region (PAR), which contains genes that are inherited just like any other autosomal genes. The PARs allow the X and Y chromosomes to pair and properly segregate during meiosis in males. Thus, there is little evidence that a sexually antagonistic gene contributes to rape.

According to the chase–away sexual selection model, continuous sexual conflict fosters an environment in which mating frequency and male secondary sexual trait development are somewhat in step with the female’s degree of resistance. Many male animal species have undergone numerous adaptations to induce females to mate with them. Peacock’s plume is an example of such adaptive secondary sexual traits. However, there is no biological insight into linking rape to a secondary sexual trait in human males.

During the last decade, several important genetic discoveries were made. It is now conclusively proved that human genes evolve much more rapidly than previously suggested. Some genes seem to be only 10,000 years old, and some may be even younger. The natural selection process produces the most dramatic changes in the gene pool when the environment is changing rapidly, such as when agriculture was invented or city–states rose. Thus, instead of being locked in cavemen DNA, human genes have actually evolved. These genes along with the changing environment have contributed to human nature that is variable and flexible at its core. Evolutionary psychology has sought to describe mechanisms that cause people to behave in adaptive ways (to the extent that they do). The most important category of mechanisms for producing adaptations is development —the myriad processes that take us from the genetic information that we inherit from our parents to the flesh and blood, thinking and feeling, experience–filled creatures we are today. With the help of genetics, the evolutionary psychologists have begun to look at the development of individual differences in men’s propensity to rape and a picture very different to Thornhill and Palmer’s is emerging.

When we look at the mechanisms that might predispose men to rape in more or less the adaptive way that Thornhill and Palmer describe, rape no longer seems to be “in its very essence, a sexual act.” Instead, men’s propensity to rape seems to be in large part developmentally contingent on boys’ and young men’s subjective experience of risky and uncertain environments. These are environments in which the flow of resources, especially of social and emotional types, is inadequate or unpredictable. There is abundant evidence that the early subjective experience of too much risk and uncertainty (i.e., chronic early stress or fear) predisposes young men (and women) to impulsiveness, a taste for risky activities, or a tendency to act too quickly without fully considering the consequences.

The subject of risk brings us to MAOA (Monoamine oxidase A) gene on the X chromosome that encodes MAO–A enzyme in humans. MAO–A degrades signaling chemicals in the brain, such as dopamine, norepinephrine, and serotonin; its elevated state is linked to major depressive disorder. A version of MAOA gene, MAOA–L or the “warrior gene,” results in less of the enzyme and can lead to aggressive behavior or impulsivity. Studies have linked the “warrior gene” to increased risk–taking and to retaliatory behavior. Men with the “warrior gene” are not necessarily more aggressive, but they are more likely to respond aggressively to perceived conflict. Because men have one copy of the X chromosome, a variant that reduces the function of this gene has more of an influence on them. Women, having two X chromosomes, are more likely to have at least one normally functioning gene copy, and variants in women have not been studied as extensively. The linking of genes to specific human behavior is just beginning.

James Dabbs of Georgia State University studied 4,462 men in 1990 and found that a combination of high testosterone —the primary male sex hormone from the androgen group bound to AR (androgen receptor) gene located on the long arm of the X chromosome — and growing up under difficult, stressful conditions was associated with having significantly more sex partners and a lower likelihood of ever marrying — but among the men who did marry, a significantly higher incidence of extramarital sex and violence against wives. These findings are doubly intriguing because men who grew up under more difficult conditions were also more likely to have high testosterone levels.

A study, published in December 2012, by the Centre for Cellular and Molecular Biology of Hyderabad, India, reports that short repeats of the DNA segment, CAG (cytosine, adenosine and guanine), in the AR gene has been observed in men prone to crimes like rape and murder. On an average, the CAG repeats 21 times in normal people and 18 or less number of times in those with criminal disposition. (Note: The number of CAG repeats in the AR gene ranges from fewer than 10 to about 36.) The study involved 400 men convicted of rape or murder or both. Psychogenetic analysis of a rapist’s mind, the study says, reveals that it is the environment (abiotic) that plays a key role in activating the genes and anti–social personality disorder in the person.

Of course, none of this ‘genetic logic’ is conscious, nor does it constitute moral justification for rape, but the evolutionary theory does provide a deeper understanding of the phenomenon. Most obviously it explains why rape is an almost exclusively male crime — there is a gross imbalance regarding the commodity value of sexual services for men and women respectively. Secondly, it is consistent with the characteristics of typical rapists — young, virile, high in sex drive, lacking in impulse control, low on the social ladder and likely to have a history of burglary. Thirdly, this theory predicts the characteristics of the typical victim — young, sexually attractive, fertile and vulnerable.

The point is that human rape at the very least is about high levels of testosterone and impulsiveness, the all–too–common consequences of living in risky and uncertain environments. And it is in precisely such environments that the most pressing adaptive problem would be passing on one’s genes. When the flow of resources is inadequate or unpredictable, the risk of death is high. When the future is objectively risky and unsure, it can be evolutionarily rationale to take even huge risks for just a small chance at passing on one’s genes. This phenomenon has been observed in several species, most notably in scorpion flies.

If rape is not all about sex then Thornhill and Palmer’s policy of preventing rape by having women dress more sensibly is not likely to “really work.” On the other hand, if rape is even partly about growing up under conditions of chronic risk and uncertainty, where access to material and social–emotional resources is inadequate and unpredictable, then maybe we should think of ways to reduce the risk and uncertainty that people encounter while they are growing up. If inequality (including power differentials) is the major source of risk and uncertainty in peoples’ lives then perhaps we should reduce inequality. Of course we didn’t need evolutionary theory to tell us that inequality is wrong, but it’s gratifying to discover that it offers reason to believe that by reducing inequality we might reduce the incidence of rape. Our only scientific theory of life, far from being the racist, sexist brute of fearful imaginations, can help us think of even more ways to identify and realize our deepest social and political goals.

Subhodev Das

  1. A lot of work you have done; I personally learnt a few things today. For example, “rapists are “extreme” individuals who tend to blend well into their own communities” … “The male rape gene would be located on the Y chromosome”. VAW such as an acid attack or that bullet that hit Malala seem to be crimes unrelated to the rape gene, right? If so, we may seek treatment for one and education and policing for the other.Am I on the right track here?

  2. The causes of VAW are rooted primarily in the abiotic environment of the genome. It is hoped that some day science will have answer for human behaviors linked to genetic expression and subsequently treatments of ‘misbehavior’ just as cancer, heart ailment and a plethora of diseases.Till then, education and policing are the only options. I tried to cast ‘epigenetics’ as a piece of the puzzle underlying human behavior.

  3. Aparajita Sen permalink

    Ah Subhodev, excellent article. Had to read it once more to really understand the issues. I am totally in awe!

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